Duration extender variable valve actuation

ABSTRACT

A hydro-mechanical variable valve actuation (or VVA) system that controllably extends the valve duration. 
     The valve opens up to its maximum lift mechanically/conventionally. 
     The hydraulic part of the system controllably retards the closing of the valve, and takes part only during the valve-closing phase.

This invention relates to a hydro-mechanical variable valve actuation (or VVA) system that controllably extends the valve duration.

FIG. 1 shows the valve lift versus the time, for the operation of an engine at 1000 rpm and at 5000 rpm.

FIG. 2 shows the valve lift versus the time for the case of heavy load at 1000 rpm.

FIG. 3 shows the valve lift versus the time for medium load at 1000 rpm.

FIG. 4 shows the valve lift versus the time for light load at 1000 rpm.

FIG. 5 shows the valve lift versus the time for idling at 1000 rpm.

FIG. 6 shows the valve lift versus the time for various loads at 5000 rpm. In FIGS. 2 to 6 it is marked by dashed line the valve lift for the case where the hydraulic system is disengaged and the valve closing is controlled by the cam.

FIG. 7 shows the basic mechanism in the case of roller finger follower valve train with hydraulic lash adjusters. The parts are sliced to show the details.

FIG. 8 shows what FIG. 7 with the parts not sliced.

FIG. 9 shows the mechanism of FIG. 7 from various viewpoints and exploded.

FIG. 10 shows the basic mechanism in the case of a valve train with bucket lifters.

FIG. 11 shows more details of the mechanism of FIG. 10.

FIG. 12 shows the basic mechanism applied on a side cam Vee engine.

FIG. 13 shows a modification of the mechanism of FIG. 10.

FIG. 14 shows the operation principle as compared to the prior art, at right.

The closest prior art is the multiair system of Fiat, U.S. Pat. No. 6,918,364, a lost motion hydro-mechanical VVA currently in mass production, wherein a cam opens the valve indirectly by means of a fluid interposed “in series” between the valve and the cam: the cam by a plunger displaces the fluid, and the fluid displaces the valve. A solenoid valve is opened the right moment allowing the fluid to escape and the valve to close, reducing either the duration or the duration and the lift. The inherent elasticity and play of the “hydraulic” system, the high loads it undergoes, the sensitivity to leakage, the need of additional means for the smooth landing of the valves, the need for additional restoring springs are some of the problems of the prior art.

In the present invention the valve opens up mechanically/conventionally to the maximum lift, under the action of a cam of a camshaft. The hydraulic part of the system controllably retards the closing of the valve, and takes part only during the valve-closing. The opening of the valve causes the displacement of a plunger slidably fitted into an oil-chamber. Oil enters into the oil-chamber through a one-way-valve or other type of valve. During the valve closing, the pressure of the oil into the oil-chamber increases. The trapped oil reacts to the force from the valve spring to the valve and to the plunger, disengaging the valve from the cam. The valve closes later, under the restoring action of the valve spring, dew to the damping action of the oil escaping out of the oil-chamber. A release-valve, for instance a solenoid on-off valve, opens at the right moment (i.e. at the right crank angle) to allow the quick escape of oil from the oil-chamber. With the release-valve open, the valve restores quickly under the action of the valve spring, pressing the oil out the oil-chamber. The conventional lubrication system is adequate to feed the oil chamber with oil.

For the smooth “landing” of the valve on the valve seat, the damping action of the oil escaping from the oil-chamber increases a little before the landing of the valve, as much as necessary; for instance by the progressive covering of the discharge port by the plunger. The shape of the discharge port can be properly designed to match with the desirable landing characteristics (acceleration, jerk etc) and to compensate for fabrication etc inaccuracies. I.e. the system has a simple and effective built-in ability to smooth out the landing of the valve.

The valve duration is equal or longer than the duration defined by the cam. With a cam having 220 degrees duration, the actual duration of the valve opening can be anything over 220 degrees, i.e. the system controllably extends the valve duration without effecting the valve lift.

With reference to FIG. 13: a cam (2), mounted on a camshaft (1), has an opening contour (3) and a closing contour (4); the cam (2), the valve (5) and the cam-follower valve actuator assembly (6) translate the opening contour (3) into a theoretical opening valve lift pattern (7) and the closing contour (4) into a theoretical closing valve lift pattern (8); a valve spring (9) restores the valve (5); an oil-chamber (10) has a release-valve (11); a plunger (12) is slidably fitted into said oil-chamber (10); the plunger (12) seals said oil-chamber (10); the plunger (12) is embodied to the cam-follower valve-actuator assembly (6); the plunger (12) under the pressure inside the oil-chamber (10) retards the restoring motion of the valve according a control unit (13) that controls the release-valve (11); the valve opens following substantially the theoretical opening valve lift pattern and closes substantially retarded relative to the theoretical closing valve lift pattern, under the control of the release valve.

The system enables the engine to get rid of the conventional throttle valve.

The breathing of the engine depends on the timing of the release-valve, i.e. on the duration of the suction cycle. The suction cycle starts at the moment the intake valves of the cylinder open and ends at the moment the intake valves of the cylinder close, where the actual compression begins.

An early actuation of the release-valve, for instance 50 degrees after BDC, increases the quantity of air trapped into the cylinder. A late actuation of the release-valve, for instance 140 degrees after BDC, allows a part of the air originally suctioned into the cylinder to return back to the intake manifold, thereby reducing the pumping loss. The increased turbulence and swirl of the charge entering and leaving the cylinder enables faster, cleaner and more efficient combustion.

For example, the suction cycle can continue until 140 degrees after BDC enabling the engine to idle at 600 rpm. This is because most of the charge suctioned into the cylinder through the wide open intake valves is pushed out of the cylinder as the piston moves towards the TDC with the intake valves still open. The duration of the suction cycle is the key parameter for the control of the engine. With the suction cycle ending earlier, for instance at 90 degrees after BDC, a good part of the working medium is trapped into the cylinder and the engine operates at medium load. With the suction cycle ending even earlier, for instance at 30 degrees after BDC at 2000 rpm or at 70 degrees after BDC at 7000 rpm, the engine makes its peak torque at the specific revs.

The same system is applicable on the exhaust valves, too, if desirable. The cam opens the exhaust valve in the conventional way, while the oil-chamber with the release-valve control the closing of the valve. Because of the heavy forces during the opening of the exhaust valve, dew to the pressure into the cylinder, most of the state-of-the-art VVAs (mechanical, electromagnetic, hydraulic etc) avoid or fail to deal with the exhaust valves, limiting themselves exclusively to the intake valves. The present hydro-mechanical system, which is not sensitive to leakage, can control the exhaust valves too, because its “hydraulic” part deals exclusively with the control of the valve closing, thereby the strong force necessary to start opening the exhaust valve does not act on the hydraulic system.

The ECU (electronic control unit) of the engine triggers each release-valve independently. Without a signal from the ECU, the release-valve stays open allowing the oil to escape quickly from the oil-chamber, i.e. the default or “safety” mode for a release-valve is “open”. This protects the engine in case of ECU (or other) failure: the system operates in the pure mechanical way, with the cam controlling not only the opening but also the closing of the valves. Each release-valve receives a pulse from the ECU. The release-valve closes at the beginning of the pulse and stays closed till the end of the pulse. In the simplest case, the ECU generates, per release-valve and per two rotations of the crankshaft, a pair of time values T1 and T2 and feeds the release-valve with a pulse starting at T1 and ending at T2. The independent control of each release-valve by the ECU allows a simpler, yet precise and effective control over the engine. Even in case there are differences from cylinder to cylinder (for instance because of a different flow capacity of the release-valves or because of a poor valve lash adjustment) the engine can still operate clean and smooth because the ECU aligns independently, based on the feedback it receives, the pulses to the release-valves.

Instead of fighting with the accuracy of the constituent parts, the ECU has the potential to rectify the operation. The old, difficult and expensive mechanical control turns to an easy and cheap digital control.

With the system proposed, an engine can operate either according the over-expansion Atkinson/Miller cycle for economy/low emissions, or it can operate according the conventional cycle for high specific torque. When combined with a Variable Compression Ratio system, like those disclosed in the U.S. Ser. No. 12/553,975, U.S. Ser. No. 12/546,714 and U.S. Ser. No. 12/404,355, the overall result is an actually variable capacity engine capable to constantly operate at optimum thermodynamic efficiency.

Applied on a Diesel engine, this system enhances the volumetric efficiency when it is advantageous, controls the actual compression ratio, controls the overlap by the retardation of the exhaust valve closing, enables the controllable exhaust gas recirculation, etc.

In a first preferred embodiment, FIGS. 7 to 9, the roller finger follower, under the camming action of the cam, pushes the valve to open; the roller finger follower is linked to a plunger by a pair of rods; the plunger is slidably fitted into an oil-chamber located beside the hydraulic lash adjuster; oil through a one-way-ball-valve fills the oil-chamber; when the valve starts restoring, the plunger into the oil-chamber moves upwards and presses the oil that has no way to escape; the oil pressure into the oil-chamber increases and the valve is disengaged from the cam (FIG. 7, third from left); the valve closes slowly under the restoring action of the valve spring and the leakage from the oil-chamber; the right moment the ECU sends a pulse to the release-valve to open, allowing the quick restoring of the valve under the action of the valve spring; as the valve approaches the valve seat, the passage of the oil decreases, because the plunger progressively covers the opening through which the oil escapes out of the oil-chamber, and the landing of the valve is smooth. In the state-of-the-art they are described other ways for the smooth landing of the valve.

In a second preferred embodiment, FIGS. 10 and 11, the oil-chamber is formed between a narrowing of the bucket lifter and the cover/guide of the bucket lifter; the plunger is embodied to the bucket lifter; the small cylinder inside the bucket lifter is the lash adjuster (either mechanical or hydraulic); the bucket lifter with the plunger and the valve lash adjuster constitute the cam-follower valve-actuator assembly; during the restoring of the valve, the pressure of the oil trapped into the oil-chamber increases disengaging the bucket lifter and the valve from the cam; for the rest it operates as the first preferred embodiment.

In a third preferred embodiment, FIG. 12, the bucker lifters between the push rods and the camshaft are similar to those shown in the second preferred embodiment. In a Vee engine with a central cam, or side cam, the long and inevitably flexible linkage from the cam to the valve reduces the accuracy of the valve motion. Yet the ECU, based on the feedback from the engine can compensate for the misalignment between the cylinders, enabling smoother and cleaner operation. At low revs and loads the engine takes advantage of the low pumping loss and the over-expansion, while at high revs and heavy loads the control of the valve duration optimizes the volumetric efficiency.

In a fourth preferred embodiment, FIG. 13, the mechanism of the second preferred embodiment is slightly modified. The one-way-valve is removed. The release-valve is open during the opening of the valve, allowing oil to fill the oil-chamber. As long as the release-valve stays open, the cam controls the restoring of the valve. When the release-valve finally closes, the valve is disengaged from the cam and restores under the control of the release-valve and of the plunger.

In a fifth preferred embodiment, FIGS. 7 to 11, the release-valve is an analog valve and needs not to open and close during every suction cycle. For instance, at 2000 rpm and medium load the ECU keeps ⅛ open the release-valve, while at 2000 rpm and full load the ECU keeps ¼ open the release-valve.

The release valves can be of any type of the state of the art, for instance on-off solenoid valves. The loads the release-valves of this invention undergo and their flow capacity are smaller in comparison with the loads and the flow capacity of the release-valves of the closest prior art, i.e. the existing mass production solenoid on-off valves are more than adequate for the realization of the present invention.

Although the invention has been described and illustrated in detail, the spirit and scope of the present invention are to be limited only by the terms of the appended claims. 

1. A variable valve actuation system comprising at least: a camshaft (1); a cam (2) mounted on said camshaft (1), said cam (2) having an opening contour (3) and a closing contour (4); a valve (5); a cam-follower valve-actuator assembly (6), said cam (2), said valve (5) and said cam-follower valve-actuator assembly (6) translate the opening contour (3) into a theoretical opening valve lift pattern (7) and the closing contour (4) into a theoretical closing valve lift pattern (8); a valve spring (9) for restoring said valve (5); an oil-chamber (10) having a release-valve (11); a plunger (12) slidably fitted into said oil-chamber (10), said plunger (12) being linked or embodied to said cam-follower valve-actuator assembly (6); a control unit (13) for controlling said release-valve (11), characterized in that: the valve opens following substantially the theoretical opening valve lift pattern; the plunger, pressed by oil trapped into the oil-chamber, retards the restoring of the valve so that the valve closes controllably retarded relative to the theoretical closing valve lift pattern, according the state of the release-valve.
 2. A variable valve actuation system according claim 1 characterized in that during the valve closing, the plunger progressively covers an opening of the oil-chamber through which oil escapes, so that the damping action of the oil increases, so that the valve closes smoothly, quietly, without bouncing and in time.
 3. A variable valve actuation system according claim 1 wherein the oil pressure into the oil-chamber during the valve closing is substantially higher than the oil pressure into the oil-chamber during the valve opening.
 4. A variable valve actuation system according claim 1 wherein the release-valve is an on-off solenoid valve electronically controlled.
 5. A variable valve actuation system according claim 1 wherein the release-valve is an analog valve.
 6. A variable valve actuation system according claim 1 that retards the closing of the valve so that to maintain it open after the bottom dead center until the unnecessary part of the charge that has entered into the cylinder is pushed out by the piston, so that the engine operates controllably at the desirable load.
 7. A variable valve actuation system according claim 1 that controls the breathing of a variable compression ratio engine in order to provide a substantially variable capacity engine, thereby an engine capable to operate permanently at optimum thermal efficiency.
 8. A variable valve actuation system comprising at least: a valve; a cam dictating a basic restoring pattern for said valve to follow during valve closing; a hydraulic means resisting to the closing motion of said valve; an on-off solenoid valve, said hydraulic means applying a strong or a weak resistance to the closing motion of said valve according the state of said on-off solenoid valve, so that by controlling the timing of the on-off solenoid valve the actual restoring pattern of the valve extends controllably beyond the basic restoring pattern.
 9. A variable valve actuation system according claim 8 wherein for the smooth landing of the valve on a valve seat, the hydraulic means comprises means that substantially increase its damping action as the valve approaches the valve seat.
 10. A variable valve actuation system comprising at least: a cam having an opening contour and a closing contour; a valve; a cam-follower valve-actuator assembly for displacing said valve under the camming action of said cam; said cam, said valve and said cam-follower valve-actuator assembly translate said opening contour into a theoretical opening valve lift pattern and said closing contour into a theoretical closing valve lift pattern; an oil-chamber having a controllable release-valve; a plunger slidably fitted to said oil-chamber, said plunger pressed by the oil trapped into said oil-chamber retards the valve closing, the valve opening substantially follows the theoretical valve lift pattern, whereas the actual valve closing pattern envelopes the theoretical closing pattern, so that the valve duration is controllably extended. 